The present invention relates to suspension dampers for vehicular applications and more particularly, to twin-tube suspension dampers with a cylinder tube end assembly controlling fluid flow between the two tubes.
Conventional vehicle suspension dampers typically consist of direct double-acting telescopic hydraulic passive dampers. They are generally described as either shock absorbers or struts. A primary purpose of shock absorbers is to dampen oscillations of the vehicle's suspension springs. This is accomplished by converting kinetic energy in the form of motion between the sprung and unsprung masses of the vehicle into heat and then dissipating the heat. Struts also serve this capacity and in addition act as a structural member to support reaction and side load forces on the suspension system.
Typical dampers are hydraulic devices using oil as the medium for converting motion into heat. As the damper is cycled by the suspension system a piston is forced to move in extension and compression directions through oil contained within a cylinder tube. This creates pressure within the cylinder tube and a consequent pressure drop across the piston. During an extension stroke, high pressure is created in the extension chamber of the cylinder tube above the piston forcing oil to flow through valving in the piston.
During a compression stroke, high pressure is created in the compression chamber of the cylinder tube below the piston, forcing oil to flow back through the piston's valving. As the piston moves an amount of oil equal to the volume of the piston rod entering or exiting the cylinder tube is forced through the piston valving or through a compression valve assembly in the base of the cylinder tube in combination with the piston valving.
Twin-tube dampers provide a reservoir between the cylinder tube and a reservoir tube which often carries a pressurized gas charge and serves as a means of compensating for the cycling of the piston rod into and out of the cylinder tube. The pressurized gas charge may also assist in the flow of fluid from the reservoir into the cylinder tube.
In order to house the damper as thus far described, a tube having a completely closed bottom portion is generally provided. The top end of the tube generally includes an opening through which the piston rod extends and provides a means of sealing the area of the opening around the piston rod. Various techniques are presently used to close the ends of the tubular sections for suspension dampers.
One conventional method is to place a base cup in the bottom end of the tube and seal the base cup to the tube by means such as gas metal arc welding or resistance seam welding to complete the bottom closure. These welds are conventionally used because they produce a strong and leak-free joint. Other methods of closing the tube section include passing the tube through a series of extrusion processes with intermediate annealing operations to produce a tubular closed end from a solid steel blank. Additionally, hot-forming a tube by means of an external forming tool is known.
Twin-tube type dampers generally include a base cup that is used to locate various internal components such as the cylinder tube by engaging the cylinder tube end assembly and the rod guide. In addition, the base cup supports the internal loading on both components for the proper functioning of the twin-tube type damper assembly.